The present invention generally relates to vehicle attitude angle sensing, and more particularly, to low-cost roll and pitch angle estimation for a vehicle.
Future generation automotive vehicles may increasingly employ safety-related devices that deploy in the event that the vehicle rolls over to provide added protection to the occupants of the vehicle. For example, upon detecting a vehicle rollover condition, a pop-up roll bar can be deployed such that, when activated, the roll bar further extends vertically outward to increase the height of support provided by the roll bar. Other controllable features may include actuating deployment of one or more air bags, such as front or side deployment air bags, or actuating a pretensioner to pretension a restraining device, such as a seat belt or safety harness, to prevent occupants of the vehicle from ejecting from the vehicle or colliding with the roof of the vehicle.
In the past, basic rollover sensors have been employed in automotive vehicles to measure the angular position of the vehicle from which a rollover condition can be determined. The basic rollover sensors have included the use of a pendulum normally hanging vertically downward due to the earth's gravitational force. Many basic automotive sensing devices are employed simply to monitor the angular position of the vehicle relative to a level ground horizontal position. As a consequence, the basic automotive vehicle rollover sensors have generally been susceptible to error when the vehicle travels around a turn or becomes airborne, in which case the earth's gravitational force, which the sensor relies on, may be overcome by other forces.
More recently, sophisticated rollover sensing approaches have been considered. One such approach considered requires the use of six sensors including three accelerometers and three angular rate sensors, also referred to as gyros, all of which are employed together for use in an inertial navigation system which tracks position and attitude of the vehicle. The three accelerometers generally provide lateral, longitudinal, and vertical acceleration measurements of the vehicle, while the three gyros measure pitch rate, roll rate, and yaw rate. In sensing a rollover condition, the system determines a vehicle roll angle. However, the more sophisticated conventional rollover sensing approaches generally require a large number of high-precision and expensive sensors. In addition, known sophisticated systems are susceptible to cumulative drift errors, and therefore must be reset occasionally.
It should be appreciated that various other applications may require knowledge of the roll and pitch attitude angles of a vehicle as the vehicle maneuvers on the ground. In addition to rollover detection, attitude angle estimators may be employed to provide a roll and pitch angle indications to the driver or other occupants of the vehicle. In the past, attitude angle estimators have employed one or more accelerometers and an angular rate sensor for each axis of rotation of the vehicle. However, there exists the problem of how to combine angle-related information contained in the accelerometer and angular rate sensor in order to obtain an overall attitude angle measurement. This is because each type of sensor generally has characteristic failings in the conventional applications. For example, the accelerometer-based attitude angle estimate is generally relatively noisy when the vehicle is traveling on a rough road surface, and may sustain large errors whenever the vehicle's trajectory involves an inertial acceleration having a component perpendicular to the rotational axis under consideration. In addition, the angular rate sensor estimate, which is typically obtained by integrating the angular rate sensor's output signal, generally has a tendency to drift with an ever-increasing error due to unknown bias or offset in the sensed angular rate signal.
It is, therefore, one object of the present invention to provide for an attitude angle estimator that provides an estimation of the attitude angle of a vehicle and minimizes errors that may be present in automotive-grade sensors. It is another object of the present invention to provide for an attitude angle estimator that combines vehicle sensed signals to obtain an overall more accurate attitude angle estimation. It is a further object of the present invention to provide for a vehicle roll angle estimator and/or vehicle pitch angle estimator that minimizes the effects of noise present in an accelerometer based angle estimate, and minimizes error present in an angular rate sensed signal.